Oncogenic mutant ras proteins have less GTPase activity and are more potent in inducing cellular DNA synthesis as compared to their normal counterpart. By analogy with G-proteins, ras proteins have been postulated to be involved in the control of growth factor receptor-mediated signal transduction, although the biochemical pathway influenced by ras proteins has not been fully understood. Using Xenopus oocytes as a model system, we investigated the possible involvement of ras proteins in the pathway leading to phosphorylation of the ribosomal S6 protein, which is related to the initiation of protein synthesis. Our results indicate that (1) microinjection of oncogenic T24 ras protein markedly stimulates S6 phosphorylation on serine residues in oocytes whereas normal ras protein is without effect, and (2) injection of anti-ras monoclonal antibody Y13-259 inhibits insulin- induced S6 phosphorylation suggesting that ras proteins mediate insulin-induced S6 phosphorylation. In another set of experiments, we have demonstrated that injection of protein kinase C promotes the induction of S6 phosphorylation and oocyte maturation by insulin or oncogenic ras protein. These findings are extremely interesting, implying that biochemical pathways regulated by an insulin receptor, ras, and protein kinase C seem to converge on S6 phosphorylation.